using System;
using System.Diagnostics;
using System.Windows.Input;

namespace MVVM
{
    /// <summary>
    /// Class used for function calls in view models.
    /// </summary>
    public class RelayCommand : ICommand
    {
        readonly Action<object> _execute;
        readonly Predicate<object> _canExecute;

        /// <summary>
        /// Creates a new command that can always execute.
        /// </summary>
        /// <param name="execute"></param>
        public RelayCommand(Action<object> execute)
            : this(execute, null)
        {
        }

        /// <summary>
        /// Creates a new command.
        /// </summary>
        /// <param name="execute"></param>
        /// <param name="canExecute"></param>
        public RelayCommand(Action<object> execute, Predicate<object> canExecute)
        {
            if (execute == null)
                throw new ArgumentNullException(nameof(execute));

            _execute = execute;
            _canExecute = canExecute;
        }

        /// <summary>
        /// Executes the Action.
        /// </summary>
        /// <param name="parameter"></param>
        public void Execute(object parameter)
        {
            _execute(parameter);
        }

        /// <summary>
        /// Used to check whether command can be executed.
        /// </summary>
        /// <param name="parameter"></param>
        /// <returns>True if command can be executed.</returns>
        [DebuggerStepThrough]
        public bool CanExecute(object parameter)
        {
            return _canExecute == null || _canExecute(parameter);
        }

        /// <summary>
        /// Raised when value of CanExecute changed.
        /// </summary>
        public event EventHandler CanExecuteChanged
        {
            add
            {
                if (_canExecute != null)
                    CommandManager.RequerySuggested += value;
            }
            remove
            {
                if (_canExecute != null)
                    CommandManager.RequerySuggested -= value;
            }
        }

        /// <summary>
        /// Must be called when CanExecute should be reevaluated.
        /// </summary>
        public void RaiseCanExecuteChanged()
        {
            CommandManager.InvalidateRequerySuggested();
        }
    }
}